It is known (German Offenlegungsschrift No. 2,031,292) that solid and homogeneous polyurethane moldings may be produced by reacting substantially stoichiometric quantities of organic polyisocyanates and organic polyhydroxy compounds, provided that precautions are taken to ensure that the reaction mixture is substantially anhydrous and has a low content of compounds which are able to liberate CO.sub.2 by reaction with the polyisocyanate compound. It is also known from the above-mentioned prior publication that the resulting polyurethane moldings may be made soft and elastic or hard by using particular polyhydroxy compounds and/or polyisocyanates.
A major disadvantage of this process is that, the solid moldings have to be heated in the mold for prolonged periods of up to 45 minutes at temperatures in the order of 100.degree. C. Accordingly, this process is attended by distinct disadvantages so far as industrial mass production is concerned.